This invention relates to improvements in an internal combustion engine equipped with a blow-by gas recirculation system arranged to recirculated or feed blow-by gas inside a crankcase through a valve operating chamber of a cylinder head to an intake system, particularly the improvements in the blow-by gas recirculation system having a flow passage structure in which blow-by gas is introduced for each cylinder through an outside piping located outside an engine main body.
As disclosed in Japanese Patent Provisional Publication No. 8-200033, it is well known that blow-by gas of an internal combustion engine is recirculated or fed from a blow-by gas output formed in a cylinder head cover through the outside piping such as a rubber hose to an intake air passage for each cylinder.